MECHANISM OF PSORALEN PHOTOSENSITIZATION AND INVIVO BIOLOGICAL ACTION SPECTRUM OF 8-METHOXYPSORALEN

[摘要] The excitation fluorescence and phosphorescence wavelengths in eleven furocoumarins are reported. The activating or exciting wavelengths for fluorescence and phosphorescence of furocoumarins were in the region of 350-365 m[mu]. The wavelengths emitted during phosphorescence were longer than those emitted during fluorescence. The long-lived phosphorescence and its quenching by molecular oxygen, several quinones, EDTA, potassium iodide and ferrous sulfate indicate that psoralen and other furocoumarins, besides exhibiting fluorescence, undergo electronic transition from the singlet excited state to the metastable triplet state. Solutions of 8-methoxypsoralen in various solvents were irradiated with ultraviolet light (> 320 m[mu]) at the temperature of liquid oxygen and examined with an electron-resonance spectrometer for free-radical formation. It appears that furocoumarins such as 8-MOP generate free radicals in solvents in the presence of ultraviolet radiation. The in vivo biological action spectrum of 8-methoxypsoralen in the skin of guinea pigs and fair-skinned humans was investigated. The data indicate that the action spectrum of 8-MOP lies in the region of 340-380 m[mu] with maximal effectiveness at 360 m[mu]. It is proposed that the mechanism of biological photosensitization evoked by psoralen involves excitation of the molecule to a singlet excited state, followed by a transition to a metastable triplet state. Psoralen molecules in the triplet state generate free radicals which more possibly evoke biological changes in the irradiated system.